Vehicle wheeled devices such as unicycles are statically unstable in all directions and thereby require dynamic balancing during riding. Two wheeled vehicle devices such as bicycles or motorcycles are statically stable in the axial direction of their advance but require balance from the rider mainly in the lateral direction. Four wheeled vehicle devices are statically stable in both the lateral and axial direction and thereby do not require balancing at all.
Vehicle wheeled devices may in some cases include means that assist in the stabilizing of and balancing of the device. Such means may be in the form of additional wheels that engage the ground when the device is un-balanced, or in more complex cases computerized controllers that in return to signals received from sensors control the balance of the device.
PCT Patent publication No. 2005100139 describes a foot-propelled wheeled device which has a wheel situated between two side-plates suspended on the axle of the wheel. Foot-boards that are situated below the axle of the wheel are connected to the side-plates and at a certain distance behind the wheel there is a structure for ensuring stabilization against tilting.
US patent publication No. 2005241864 describes a motorized vehicle that has a plate-like main body with front and rear side support plates and a wheel that is arranged on the bottom surface of the main body. The wheel preferably includes a motor, and a drive controller is preferably embedded in the main body for receiving signals from sensors that are located in the vehicle in order to control the motor and thereby help balance a user riding the vehicle.
U.S. Pat. No. 4,657,272 describes a wheeled vehicle comprising a unicycle-like device. The device employs a single large drive wheel, a pair of pedals, a seat, and a pair of forks to support the seat and attached to the rear of the device is an additional set of support wheels. The support wheels are attached to the device in such a manner that they track through turns as the drive wheel is turned to the right or left and under normal conditions the support wheels remain on the ground at all times to provide the rider with additional longitudinal stability without adding a significant increment of lateral stability.